Yes Ian! Ainsley an I were aware of that. But Ainsley has a large selection of large bearing outer races and found one that made a good all-round the bore support. I've just come in from completing 52 running in miles and it's a lot smoother.
The bigger piston was also giving me starting problems. Nothing to do with the higher compression of course, as the valve lifter takes care of that, But whether it was sucking in more fuel or something else....I just don't know, but I spent quite some time kicking on odd occasions and even changing the plug.:thinking_face: Ron
['Very nice, Ron...In a way, I'm quite pleased to hear that the big-bore long stroke way doesn't necessarily make for a nicer motorcycle. Val Page and his colleagues knew what they were doing...']
Val Page is my favourite designer without a doubt and many of his designs are represented amongst the more practical motorcycles..In fact I have his picture on my workshop wall....
However, I would suggest that, by any measure, my oversized M20 is an improvement on the original specification in terms of its performance for long distance touring and for use under modern road conditions, along with the additional bonus of improved fuel consumption due to the increased efficiency of the overall layout bought about by the changes..
Simply enlarging an engine to improve its power without any other consideration of its specifications and how the changes will affect its operation and overall characteristics is an over simplistic approach and one that may, or may not, result in a better machine...It's purely down to chance based on the components used and the subject engines specifications....
As Trevor notes crankshaft balance is key in this situation...I have built 720cc M20s (and other capacities) both with and without rebalanced crankshafts and the former results in a very sweet and smooth engine...In fact it is often the case that the performance of an original standard crank assembly can be much improved by applying modern balancing methods, as original production tolerances and methods were frequently not as accurate...With Royal Enfield twins as a notable exception most companies statically balanced their cranks...Dynamically balancing them is a more accurate method used my most companies offering that service currently...
I appreciate the original designs as much as anyone and also appreciate there is a valid argument for wanting the 'original' experience provided by using a standard specification engine but in reality all designs can be improved upon to suit individual requirements and the only reason some don't do it is simply because they've made the choice not to...Ian
Ever since I had the A65 balanced @ 4500 rpm it has become SOP on every engine rebuild
BEst $ 200 any one can spend
Now I would not pull a good engine down to get it done but if the crank has to come out then it is a trip to the heat treatters for a carbo nitride then another to the balancer
I killed the A65 by pretending it was an A 10 , gearing it up to get better fuel economy and a longer range.
SO the new build was balanced at 4500 so it is uncomfortable to ride under 3500 and really nice from there to 6000 which has me in license loosing land.
When I eventually get around to fitting Ians nice new big bore pistons I am looking to do a dynamic at around 3000 rpm.
In reality I should build it get it dynoed then balance to just above peak torque but on most long stroke side valves that is somewhere from 2500 to 3500
